docs: def setexternalfile(self, filename, offset=0):
          """Store the dataset data in an external file.
  
          Args::
  
            filename    external file name
            offset      offset in bytes where to start writing in
                        the external file
  
          Returns::
  
              None
  
          C library equivalent : SDsetexternalfile
                                                    """
  
          status = _C.SDsetexternalfile(self._id, filename, offset)
          _checkErr('setexternalfile', status, 'execution error')